Gas separation by adsorption process



May 24, 1966 T. M. STARK GAS SEPARATION BY ABSORPTION PROCESS FiledApril 1, 1963 I5 CHECK VALVE 2 Sheets-Sheet 1 I58 2 CHECK VALVE CHECKVALVE CHECK CHECK VALVE VALVE GRADE BED BED AA STAGE I 2 PRODUCT 4 I7 37CHECK 22 50 5| VALVE j 13 I4A CHECK CHECK |3A VALVE 39 .VALVE |8A3 GRQDEPRODUCT BED BED BED STAGE I 2 3 BED BED BED GUARD- l 2 3 49 I SOLENOIDm2 3| 3o 43 4 4s 4s 48 I 24 M Q J |e 42 .E x A IOA'\ FUEL FEED F|G.-l

Thomas M. Stork Inventor y 4, 1966 T. M. STARK 3,252,268

GAS SEPARATION BY ADSORPTION PROCESS Filed April 1, 1963 2 Sheets-Sheet2 67 66 SURGE 7s 77 TANK 7' GRADE AA 82 STAGE 2 BED 78 79 SURGE l TANKGRADE A Thomas M. Srork lnven'ror Porenr Attorney United States PatentTheinstant invention relates to a process for obtaining high purityproducts. In particular, it relates to a specific combination ofadsorbent zones operated in such a manner as to continuously produceboth an ultra pure product and a moderately pure product, thus obtainingincreased product efficiencies and yields. The preferred product ishydrogen. Even more specifically, the invention is directed to acombination of, and sequence of, adsorption and desorption processeswhere desorption is effected both by the reduction of pressure onadsorbent beds as well as by purging adsorbent beds.

I It is now known according to the teachings of US. Patent 2,944,627issued to C. W. Skarstrom, that an adsorbent, after substantialsaturation with one or more components may be desorbed by reducing thepartial pressure of that component in the atmosphere surrounding theadsorbent. US. Patent 2,944,627 also teaches that such desorptions bypartial pressure reduction can be made more efficient by rapidlypressuring and depressuring so that the heat of adsorption is notallowed to dissipate throughout an adsorption bed and is available tocontribute toward the desorption partial pressure effect.

The process of alternately adsorbing with high pressures and desorbingwith low pressures is referred to herein as AP (delta pressure), i.e.,AP cycles. In AP cycles, the pressure reduction at the beginning of thedesorption step can be carried out in a variety of ways. For example,where the adsorption process is carried out for the purpose of obtaininga pure efliuent, and where adsorption is conducted at superatmosphericpressure, the saturated adsorbent may be merely vented to theatmosphere. If it is desired to retain the adsorbed material, in suchsuper- .atmospheric operation, the venting may be into a closed vesselthus permitting the recovery of adsorbed material. Passages orpassageways through which bed pressures can be reduced can be located atany convenient place on the periphery of the bed or adsorption zone.

Moreover, whether adsorption is conducted at super atmospheric,subatmospheric or atmospheric pressure, desorption can be accomplishedby use of a vacuum.

The use of the above-described desorption technique has advantages overthermal cycles. Primarily their advantages are the elimination ofheating and cooling. A fast cycle can be employed because no time isrequired for heating and cooling the bed.

In essence, heatless adsorption is a solid adsorbent, gaseous,separation process involving continuous cyclic operation withoutapplication of external heat for regeneration of the adsorbent. Thisheatless aspect is attained by using the generated heat of adsorption asthe thermal driving force in the regeneration step. Removal of adsorbedgas from the bed during regeneration is achieved by lowering pressureand sweeping the adsorbent with a purge stream of product.

Although there is substantially no net transfer of heat to and from thebeds in the preferred method of operation it will be understood thatcontrol of the ambient temperature is contemplated. Thus, the adsorbentbeds'can be surrounded by a heat transfer medium so as to controlambient temperature. Alternatively, heating or cooling means can beprovided directly within the adsorbent bed. Such means, for example, canbe conducting means for electric current or conduit means for carrying aheat transfer medium directly within the adsorbent bed.

It follows that when the ambient temperature of the bed is controlled,then the temperature of the feed or other gases passing through the bedsshould be close to that ambient temperature.

Thus, if it were desired to carry out an adsorption process of theinvention for a feed at 600 F., the beds themselves would be -preferablyheated by external means to 600 F.

Although the use of the processes which depend on what are referred toas the heatless adsorber principle have recently become wellestablished, it has not hitherto been possible to obtain largequantities of an ultra pure product as well as large quantities of amoderately pure product. It has now been discovered, and forms thesubstance of this invention, that by combining at least two adsorbentzones in a certain series and parallel relationship both an ultra pureproduct as well as a moderately pure product can be obtained.

In brief, the combination of adsorbent zones is preferably in two stagesbut may also be in 3 or more stages. .Each stage has one or moreadsorbent zones. In one preferred embodiment of the invention, the firststage has three substantially identical adsorbent zones and the secondstage also has three substantially identical adsorbent zones. Theadsorbent zones in each stage are connected with a series ofinterconnecting conduits (pipes) with suitable valving. Generally ifthere is more than one adsorbent zone in a stage, the zones will have aparallel relationship with each other, while the zone or zones in onestage bear a series relationship with a zone or zones in the otherstage.

A typical operation of the process of the invention with three adsorbentzones in each of the stages is as follows. Each adsorbent bed or zonehas a feed end and a product end. A feed containing as little as 5% ofthe desired component is introduced into'the feed end of the firstadsorbent bed of the first stage. The efliuent from the product end ofthe first bed of the first stage contains a large percentage of thedesired product. The efiluent from the product end of the first stagebed is divided into two portions. One portion goes to a moderately pureproduct line for blending with depressure gas from the .second stage.The second portion is introduced into the feed end of the first bed ofthe second stage. The efiiuent vfrom the product end of the first bed ofthe second stage is an ultra pure product which will be referred toherein as a Grade AA product. The moderately pure product will bereferred to here as a Grade A product. A portion of the ultra pureproduct efiiuent emerging from the product end of the first bed of thesecond stage is used to purge the first bed of the second stage.

But prior to such purging step, the first bed of the second stage isdepressured at the feed end to allow some of the adsorbed material tocome off as depressure gas. A portion of this depressure gas is used asa component of the moderately pure product, i.e., Grade A product. Theproduct purge introduced into the product end of the first bed of thesecond stage, then desorbs the remainder of the adsorbed material. Thus,the first portion of depressure gas from stage 2 plus a portion of theproduct efiluent from stage 1 makes up the Grade A product.

The remaining portion of the depressure gas from bed l-stage 2 and purgeefiluent from bed l-stage 2 exits from the feed end of bed l-stage 2 andis used to purge l-stage 1. The purge of bed l-stage 1 is carried outafter the pressure has been reduced in bed l-stage 1.

The above is a very brief description of a basic process sequence asapplied to the #1 beds of the first and second stage and it will beunderstood that essentially the same process sequence except for bedpressure equalization would be employed if the two stages employed 2 ormore beds. Preferably three beds are used in each stage so as to have acontinuous product flow. When two or more beds are used in each stagethen preferably bed pressure equalization through the product ends ofthe beds is carried out prior to depressuring. Bed pressure equalizationcan be carried out from product end to feed end or from feed end toproduct end or from feed end to feed end. Generally from product end toproduct end is preferred. Beds 1, 2 and 3 of the first stage are in aparallel relationship with each other as are beds 1, 2 and 3 of thesecond stage. However, the identically numbered beds of each stage arein a series relationship with each other.

Additionally, depending to a certain extent on the type of feedemployed, a guard bed or guard beds can also be used between the rawfeed stream and the bed or beds of the first stage. Charcoal ispreferably used as an absorbent when H is the desired product. The guardbed will preferably contain a wide pore silica gel to preventcontaminants such as C hydrocarbons from reaching the charcoaladsorbent. Such hydrocarbons are diflicult to desorb from charcoal. Theadsorbent in the guard bed will vary depending on the feed andcontaminant.

An important feature of the instant invention is the minimization ofproduct loss in the depressure gas. It was discovered that the firstportion of gas obtained during depressuring at the product end, i.e., inthe same direction as feed flow during adsorption is rich in desiredproduct, e.g., hydrogen. Thus, when this depressure gas is used topartially repressure a bed just completing a low pressure purge,substantial product is prevented from being lost from the beds. I

In operation, a low pressure bed and a high pressure bed are connected,preferably at their product ends. The pressure between them is thenallowed to equalize. This is bed pressure equalization. Although productend bed pressure equalization is preferred, feed end bed pressureequalization can also be used. Moreover, beds can have their pressuresequalized by connecting the feed end of one bed to the product end ofanother.

Although the instant'invention can be used generally to obtain Grade AAand Grade A product from many different feed streams, the invention willbe described with reference to a specific embodiment with respect toobtaining Grade AA hydrogen having a purity of about 99.995 and Grade Ahydrogen having a purity of 99%. Almost any type of feed can be employedeven those containing as little as hydrogen. The feeds can containhydrocarbons as impurities or they can have nonhydrocarbon impuritiessuch as Co, H O, CO H S, N air and the like. The gases containing H canbe industrial type gases such as producer gas, blue gas, the gas fromthe iron steam reaction, gas from the water-gas reaction, thermaldecomposition of hydrocarbons, synthesis gas, NH decomposition gases andthe like.

It is contemplated that one of the most advantageous uses of theinvention will be to utilize hydrocarbon and hydrogen feeds such asrecycle gas or powerformer tail gas, fuel gas, catalytic cracking offgas, and the like. When using, gases having appreciable quantities oflow molecular weight hydrocarbons'such as powerformer recycle gas ortail gas, not only can a Grade AA product and a Grade A product beobtained, but a third product, fuel, can also be obtained.

Tail gas is an uncondensed reaction efiluent from a hydroformingreaction. A typical tail gas comprises a major proportion of hydrogen,i.e., about 72.5 vol. percent. The balance of a typical tail gas is madeup of light hydrocarbons in the C to 0., range although there can besome C Normally such light hydrocarbons will make up less than 50 vol.percent of the tail gas. Utilizing the process of the invention withpowerformer adsorber-stripper off-gas, a recovery of 99+% purity hydrogen was over 70%. The process can produce hydrogen as pure as 99.99%at pressures from 100 to 500- p.s.i.g. from feeds containing from 30 to99.5% hydrogen with hydrogen recoveries as high as 85%.

The invention can be fully understood by referring to both the precedingand the following descriptions, the

claims taken in conjunction herewith and by the accom panying drawingswherein FIGURE 1 is a schematic diagram of a process suitable forcarrying out a preferred embodiment of the inventive technique withthree adsorption zones in each stage.

FIGURE 2 is a schematic diagram of a process suitable for carrying out apreferred embodiment of the inventive technique using one adsorptionzone in each stage.

Powerformer tail gas from a powerformer absorberstripper is flowedthrough lines 10 and 10A and through automatic valve 11 to guard bed 1.Guard bed 1 is made up of wide pore silica gel having a pore size ofabout to 160 A., e.g., to A., which removes the C material from the feedstream so as to prevent contamination of the adsorbent in the mainadsorbent beds. The adsorbent of the main adsorbent beds is preferablycharcoal.

The C product from guard bed 1 enters the stage l-bed 1 absordent bed,through automatic valve 12 and line 12A. A portion of the efiluentproduct from the stage 1-bed1 adsorbent bed containing 99.0% H is takenoff through check valve 13 and conveyed through line 13A to the Grade Aproduct line. The remaining part of the product from stage l-bed 1enters stage 2-bed 1 through automatic valve 14 and line 14A. Theproduct from stage Z-bed 1 containing 99.995% hydrogen passes throughline 15A check valve 15, and line 153 to the Grade AA product line.

The bed 1 adsorbers of both stages remain on the adsorption portion ofthe cycle for 4 minutes and 10 seconds before they are taken oifstreamfor regeneration. After this period, the bed 1 adsorbers will be spentand the bed 2 adsorbers of both stages are automatically substituted forthem. The bed 3 adsorbers of both stages are substituted for the bed 2adsorbers after another 4 minutes and 10 seconds have passed. Eachadsorber is, therefore, on adsorption for 4 minutes and 10 secondsbefore it is regenerated. Therefore a complete cycle is accomplished in12 minutes and 30 seconds.

The #2 adsorbers of both stages are substituted for the #1 adsorbers ofboth stages by opening automatic valves 16 and 17 and closing automaticvalves 11 and 14. The first phase of the #1 adsorber regenerationrecovers some of the high purity hydrogen in the #1 adsorbers bydepressuring and equalizing the pressure between them and the #3adsorbers which at this stage of the cycle are at 0 p.s.i.g. Before thisbed pressure equalization step (BPE) is accomplished, guard bed #1 isisolated from bed I-stage 1 by closing automatic valve 12. During theBPE step, valve 24 is opened and guard bed #1 begins to depressure intoline 23. Bed l-stage 2 is isolated from bed l-stage 1 by closingautomatic valve 14. The BPE step between the bed l-stage 1 and bed3-stage 1 adsorbers is initiated by opening automatic valves 18 and 19.This allows depressure gas to flow through line 18A. The BPE stepbetween bed l-stage 2 and bed 3-stage 2 is initiated by openingautomatic valves 20 and 21. This allows depressure gas to flow throughline 20 A. These valves are closed at the completion of the BPE step.

\Following the BPE step the gas pressure in bed l-stage 6 Two-stagerepressuring is preferably utilized to minimize possible charcoalattrition.

The final repressuring of the second stage adsorption units isaccomplished with high purity H product as, for

2 has been reduced from about 190 p.s.i.g. to about 95 5 example, fromthe bed 3-stage 2 adsorber now onstream p.s.i.-g. The hydrogen gasremaining in bed l-stage 2 by opening automatic valves 20 and 21 tobring bed has a relatively high purity. This gas is recovered by1-stage2 to adsorption pressure. Valves 20 and 21 are depressuring bedl-stage 2 to the 0 p.s.i.g. H product then closed. Second stage feed mayalso be used for line through line 22A by opening automatic valve 22.final repressuring of the second stage. At about 70 p.s.i.g. valve 22closes. While valve 22 is At this step in the cycle, the #1 adsorbersand #1 open, valves 12 and 24 are also open and guard bed #1 guard bedhave been regenerated and repressured and are and bed l-stage 1 aredepressuring to line 23. When ready to be returned to absorption servicein place of valve 22 closes, valve 14 opens and the #1 beds of stage thenow spent #3 adsorbers. 2 and stage 1, and guard bed #1 continue todepressure Check valves 32 and 33 are similar in function to in seriesinto line 23. The additional quantities of gas bed 2-stage 2 and bed3-stage 2 as check valve 15 is to in guard bed #1, bed l-stage 1 and bedl-stage 2 are bed l-stage 2. Check valves 34, 35, and 36 permit thedepressured to fuel gas line 23 by opening automatic flow of high purityproduct from valves 25 to purge stage valves 14, 12 and 24. 2 beds #1,#2, and #3. Valve 37 is to bed 3-stage 2 When the pressure in the three#1 beds has reached as valve '14 is to bed l-stage 2 and valve 17 is tobed that of fuel line 23, automatic valve 25 is opened to allow 2-stage2. Valves 38 and 39 are to stage 2-beds 2 and 3, a portion of the highpurity product from the bed 2-stage as valve 13 is to bed l-stage 2.Valves 4t and 41 are 2 adsorption beds, now onstream, to purge remainingto beds #2 and #3 of stage 1 as valve 12 is to bed l-stagehydrocarbons-from the charcoal and silica gel in the #1 1. Valve 42 isto guard bed #3 as valves 11 and 16 adsorption beds. This purge streamis controlled by are to guard beds #1 and #2. Valves 43, 44, 45 and handcontrol valve 26 and rotameter 27. valves 46, 47 .and 48 are to guardbeds #2 and #3 as At the completion of the above purge step, automaticvalves 31, and 24 are to guard bed #1. Valves 50 valves 25 and 24 areclosed and the first and second and 51 are to bed 2-stage 2 and bed3-stage 2 as 22 is to stage #1 adsorbers and the #1 guard are ready tobe bed l-stage 2. repressured in preparation for going back onadsorption The valves in FIGURE 1 other than the check valves cycle. Thetwo #1 bed adsorbers are isolated from 30 are two-way solenoid valves.They are operated in a each other by closing automatic valve 14.predetermined timing sequence from electric solenoid The repressuringoperation is initiated by a BPE step program timer 49. Wiring isconventional and need not between the #1 adsorbers at fuel line pressureand the be shown. #2 adsorbers that have just been taken out ofadsorption It will be understood that although the above descripservice.(The #3 adsorbers are now onstream.) The tion of the operation does notdetail in full the operation BPE step between the #1 and #2 beds in thefirst stage of every bed, the operation of the beds not detailed will isinitiated by opening automatic valves 18 and 28. The be completelyapparent by analogy. BPE step between the #1 and #2 adsorbers in thesecond Both stage 1 and stage 2 each having three beds use stage isinitiated by opening automatic valves 20 and 29. a 4 min. 10 sec.adsorption time per bed as Well as a These valves are closed at thecompletion of the BPE step. 4 min. 10 sec. depressure and purge time foreach bed and The final repressuring of the first stage adsorption beds a4 min. 10 sec. time to repressure. For a typical operaand guards isaccomplished with feed in a two-stage tion wherein adsorption pressureis 190 p.s.i.g. and purge pressuring operation. The opening of automaticvalve pressure is 0 p.s.i.g. there will be a sequence of timed or 30initiates the repressuring operation and allows it to programmed eventstaking place on each bed during proceed at a controlled rate. When thepressure in the each 4 min. 10 sec. cycle. These sequences have threebed l-stage 1 adsorber has been raised so as to reduce components. Theseare (1) adsorption, (2) BPE, dump, the repressuring rate, automaticvalve 31 is opened to purge, and (3) BPE, repressure. Typical programmeddecrease the flow resistance and complete the repressuring. integratedcycle time relations are shown in Table I.

TABLE I B d 1 Step: Adorption BPE Dump Purge BPE Repressure Press: Psig9? 9 -4 95 5 0 o-- 95 95 1 0 Time 0 l a 1 t x l3 1b 12 (min.) i l 1 IStep: BPE Dump Purge BPE Repressure Adsorption Bed 2 32; 9 -95 o o 5 5-1 o 190 l l I Time 0 I l I 6 1 {g 10 I 12 Bed 3 Step: BPE RepressureAdsorption BPE Dump Purge 93 gig 95 95 9 9 9 g 95 0 Time 0 g l 2 i 6 I gI 12) I l2 (min.)

The material balance for atypical unit of the preferredembodiment is asfollows in Table II below.

TABLE II Material balance BPE-bed pressure equalizatin.When'two beds oradsorbent zones at different pressures are connected together to resultin the equalization of the pressures within both. Usually adsorbedmaterial from the bed or zone at high pressure will flow over and beadsorbed on the bed or zone at lower pressure. This material is referredRate Pressure oom osito as depressure gas. BPE (decrease) refers to thebed Stream gg fig or zone which decreases in pressure. BPE (increase)refers to the bed or zone which increases in pressure. Feed 82 000190430 83 Dump.When the pressure Within a bed or zone is lowered to thelowest pressure of a cycle, usually resultg3,; 2 40,700 190 230 5 ing inthe exiting of formerly adsorbed components from 99% Product 18,800190-230 99.5 the bed or zone. These components are also referred toTotal 59 500 EH30 99.5 herein as depressm'e gas. Also calleddepressuring. De- P d t 24 000 40 99 pressure gas can be eithercollected as product, used to g f etifrifiaa 24: 000 2, 500 99. 995Purge anothfir dlscarded- 1 Purge.Carr1ed out at the lowest pressure ofthe cycle j Portion 22 500 0 60 after the bed or zone has been subjectedto a BPE (de- Purge Portion 11,500 0 60 crease) and a dump. When amaterial, usually richer in Tom] 34,000, 0 60 nonadsorbable constituentsthan the feed to the zone, is flowed countercurrently to feed directionso as to cause gggfigg gig figgi 7 300 O 5 adsorbed components withinthe zone to exit with it. This Purge Portion 4,200 0 98 occurrence ispurging. The material rich in nonadsorbed Total 11,500 0 98,5constltuents is the purge gas both as it goes in and as it P d ta 5 20040 98 5 25 comes out of a bed or zone. gfili fl volf fmitreiterate;41200 0 991995 Repressure.Raising the pressure of a zone or bed to theadsorption pressure of an adsorption cycle. In the 1 Depressure andpurge effluent from stage 1. preferred process of the inventionrepressure of the first :grom sgage ginto stage 1. stage is done withfeed and takes place in a bed or zone i age after the BPE (increase)step. Repressure of the second Typlcal l S1165 and'othef P I data pstage is done with product. However, it is possible to ferred embodimentdescribed are itemized below In Table repressure i h stage with feed orproduct. 1 Although the process of the invention is particularly TABLEIII adapted to two stages with three adsorption zones each, Bed sizesand process dam for preferred unit it can also be carried out Wllll one,two or more beds (zones) in each of the stages. Multiple zones in eachstage Stage 1 stave 2 are convenient since continuous product flow canbe obtained and various storage vessels and other equipment mRecovery(percent). 85 59 can be eliminated. The number of beds per zone willgrogueg lljlate ((s.e.t .t i ./lb.) 2 1 24 3 3 depend on the complexityof the cycle and other factors 1'0 110 OW 5.0. Char Loading 1 (Lb./b ed)2, 460 9,190 aPParePt to one sklned the Char Volume (Ft. /Bed) 98 127For instance, FIGURE 2 shows a preferred embodiment gfigig 9g gfif5i1 2221 of two stages, each of which has a single bed. There is a surge tank60 for both stages and a surge tank 61 for 1 Columbia Grade ACO 6x14mesh activated. carbon 1,100 m. /gm. Stage In operatlon, e flows throughline 62 and su rface area). 1 h 4 2 I valve 63 1nto bed l-stage 1. Thefeed comprises about ,ggggg figggf z, gf ggfig 223? (3 Sm ace area) Hand the major portion of the remainder is C o C h r car ns. there ar larua 'tie It will be understood that the exact process conditions a g g glg g a wide g Z 2% Zi g;

. v 4 under .Whlch the concefpt of the lnvenuon can be can-led 50 gelguard bed is preferably used to take out these higher out will varydepending on the absorbent, feed stock, 1 h h d b desired purity andother adjustable factors which will be inoleeu ar Yvelg t y wear Ons soas to avol 'Contammat' ing the main adsorbent beds. apparent to oneSklnedm the Bed l-sta e 1 is ressured u to adsor tion ressure Forhydrogen recovery of relatively high purity from g p p p p with thefeed. Efiluent starts to come out of bed l-stage a hydrocarbon feedstream, the following conditions are 5r 1 and at this time it isconsidered to be on adsor tion set forth as a guide. 0 g p OperatingPreferred Especially Preferred Charcoal pore diam. A 20 to 200 20 to 0020 to 40 Silica gel pore diam. A. 100 to 200 110 to 180 120 to 160Percent H2111 Feed 5 to 99. 99 40 to 95 50 to Percent H in Grade AProduct..- 90 to 99.9 to 99.5 98 to 99 Percent H2 in Grade AA Product-99.99 to 99.9999 99. 995 to 99. 99s 99. 995 to 99. 99s AdsorptionPressure, p.s.i.g 15 to 1,000 75 to 750 100 to 500 Product Flow Rate,5.0.1 h 1 to 1,000,000 10 to 500,000 1,000 to 200,000 Cycle Time,min. 1. 5 to 30 10 to 20 12. 5 to 15.0 Temperature, F. -350 to 1,000 40to 150 70 to Depressure Time, 0.1 to 10 0. 5 to 5 1 to 3 RepressureTime, In 0.1 to 10 0. 5 to 5 1 to 3 lowing meanings:

Ads0rpti0n.When product .efiluent is actually exiting from an adsorptionzone as well as material being adsorbed within the zone, i.e., on theadsorbent in the zone. 75 sired, a portion of effluent from stage #1 canbe con- The effluent flows through line 64 and valve 65 to bed l-stage2. An extremelypure product comes out of stage #2 bed and flows throughline 66 and valve 67 to surge tank 61. .This process is continued untiljust before break through of adsorbable components of the feed. If de-69, which is a three-way valve, and valve 70 are opened so as to allowthe beds of both stages to depressure to the low pressure of the cycle.The first portion of depressure gas from stage #2 will go to surge tank60 via valve 69 and line 71. The first portion of depressure gas is thepurest portion. The remainder of the depressure gas, i.e., the less pureportion, from stage #2 can be conveyed directly to stage 1 as purge gasthrough line 80, valve 69 and lines 72 and 73. Additional purge gas forstage 1 can be supplied from surge tank 60 through line 73 and valve 74.

The discharge from stage 2 which is caused by the purging of stage 2 byproduct effluent coming out of surge tank 61 and through valve 81 andline 82 through stage 2 and out line 80, is flowed through line 80,valve 69, line 72 and line 73 into bed #1 of stage 1 where it also aidsin purging bed l-stage 1 at low pressure.

Before bed 1 of stage 1 is purged as described above, valve 70 is openedto allow depressure gas to come off bed l-stage 1 through line 75 Thisgas can be used a fuel or discarded, depending on its composition.

Valve 76 is opened occasionally toallow withdrawal of Grade AA productfrom surge tank 61 through line 77.

Valve 78 is opened occasionally to allow withdrawal of Grade A productfrom surge tank 60 through line 79.

Grade A product is generally a combination of the first portion ofdepressure gas from bed l-stage 2 and product gas from bed l-stage 1.

It will be appreciated that a guard bed containing an adsorbent such assilica gel can be used in feed line 62 to prevent the beds of stage #1and stage #2 from becoming contaminated by hydrocarbons having four ormore carbon atoms -or other impurities difficult to desorb from the mainadsorbent beds. The invention will be further illustrated by thefollowing examples.

EXAMPLE 1 The beds were depressured to various pressures ranging from400 p.s.i.g. to 50 p.s.i.g. The results are summarized in the followingtable.

TABLE IV Avg. Comp. of Depressure from Gas, Percent 500 p.s.i.g. to-

H2 CH4 Feed: 80% H 7% C 7% C 6% C at 500 p.s.i.g.

It was observed in the above test that the first portion of gasobtainedwhen depressuring in the same direction as the feed duringadsorption was larger in hydrogen than the feed. This was due to thedifference between the charcoals capacity for hydrogen and hydrocarbonand the relatively slower rate of hydrocarbon desorption. The aboveresults demonstrated this and showed that the depressure gas hydrogencontent was from about 9399% when using a 80% hydrogen content feed.Thus, by connecting the outlet end, i.e., product end of two bedsfollowing a low pressure purge step on one bed and allowing them topressure equalize with upflow bed pressure equalization, i.e., productend bed pressure equalization, about half of the hydrogen previouslylost in depressur gas could be recovered.

EXAMPLE 2 In this example the eificiency of the bed pressureequalization step was demonstrated in a continuous cyclic operation.Runs using bed pressure equalization were compared with runs with no bedpressure equalization. The runs were performed at an adsorption pressureof 500 p.s.i.g., a desorption pressure of 0 p.s.i.g., a temperature of100 F. for both adsorption and desorption and a 8 min. 20 sec. cycle.The feed contained' hydrogen and the product had a purity of 99.9%hydrogen. It was discovered that hydrogen recovery was increased from avalve of about 60% to about 75%. This corresponds ap proximately to thepredicted savings of one-half of the usual depressure gas losses. Theproduct rate was about 21 s.c.f.h./lb. for both bed pressureequalization and nonbed pressure equalization. The explanation for thisis that in conventional downfiow, i.e., feed end depressuring the gasobtained is approximately of feed composi- What is claimed is:

1. In separation processes utilizing the principles of heatlessadsorption wherein adsorption of at least one component of a feed streamat a relatively high pressure and desorption of adsorbed component ofsaid feed at a relative-1y lower pressure is carried out in anadsorption zone, the improvement which comprises in combination:

(a) Flowing a feed stream into adsorbent zone A, said zone A beingselective for at least one component of said feed stream and allowing anefiluent to emerge from said adsorbent zone A.

(b) Flo-wing. at least a portion of said effluent from said zone A asfeed efliuent into adsorbent zone B, said zone B being selective for atleast one component of said feed efiluent and allowing a primaryefiluent to emerge from said zone B.

(c) De-sorbing said adsorbent zone B by first lowering the pressurewithin said adsorbent zone B to obtain a depressure gas and then purgingsaid zone B with -a portion of said primary effluent from said zone B toobtain a purge effluent.

(d) Desorbing said adsorbent zone A by first lowering the pressurewithin said adsorbent zone A and subsequently purging said zone A with apurge comprising a portion of depressured gas from zone B.

-(e) Collecting as a first moderately pure product stream a streamcomprising the eflluent of zone A and the depressure gas from zone B,and collecting as a second relatively very pure product stream theefiluent of zone B.

2. A method according to claim 1 wherein said feed tively low pressure,the resulting depressuring causing substantial quantities of adsorbedconstituents within said zone B to exit from said zone B as depressuregas.

5. A method according to claim 4 wherein in said subparagraph (d) saidpressure is first lowered to a pressure intermediate said relativelyhigh pressure and said relatively low pressure by connecting zone A toadsorbent zone D to cause some transfer of adsorbed components from saidzone A, said adsorbent zone D being at said relatively low pressure, andsubsequently depressuring zone A to said relatively low pressure byventing said zone A to said relatively low pressure, the resultingdepressuring causingsubstantial quantities of remaining adsorbedconstituents withinsaid zone A to exit from said zone A as depressuregas.

6. A separation process utilizing adsorbent zones A, B, C, D, E and Fwherein adsorbent zones A, B and C are in stage 1 and adsorbent zones D,E and F are in stage 2 which comprises in combination:

(a) Adsorbing a feed stream in zones A and D and withdrawing effluentfrom zones A and D at a relatively high pressure while simultaneously(1) Reducing a relatively high pressure in zones B and E to anintermediate pressure by connecting said zones B and E to said zones Cand F respectively, said zones C and F being at an initially relativelylow pressure wherein the pressure in said zones C and F is raised to anintermeidate pressure;

(2) Reducing the pressure of said zones B and E from said intermediatepressure to a relatively low pressure;

(3) Purging said zones B and E while zones C and F are being repressuredfrom an intermediate pressure to a relatively high pressure;

(b) Reducing said relatively high pressure in zones A and D to anintermediate pressure by connecting said zones A and D to zone-s B and Ewherein the pressure in said zones B and E is raised to an intermediatepressure, then reducing said intermediate pressure within said zones Aand D to said relatively low pressure, purging said zones A and D, and

(1) Repressuring said zones B and E to a relatively high pressure whilethe intermediate pressure reduction and purge are taking place in saidzones A and D;

(2) Adsorbing a feed stream on and withdrawing effluent from zones C andF at a relatively high pressure; 7

(c) Repressuring said zones A and D to an intermediate pressure byconnecting said zones A and D to said zones C and F, said zones C and Fbeing reduced from a relatively high pressure to said intermediatepressure, then repressuring said zones A and D to said relatively highpressure, while (1) Adsorbing a feed stream on and withdrawing efiiuentfrom zones B and E;

9. A method according to claim 7 wherein said feed stream comprises amajor proportion of H 10. A method according to claim '8 wherein saidfeed stream prior to entering stage 1 adsorbers passes through anadsorbent selective to hydrocarbons having more than four carbon atoms.

11. A method according to claim 10 wherein said adsorbent is a wide poresilica gel having a pore diameter of from 100 to 200 A.

12. A separation process utilizing a feed and adsorbent zones A, B, C,D, E, and F wherein adsorbent zones A, B and C are in a first stage andadsorbent zones D, E and F are in a second stage and wherein all of saidzones are interconnected, the zones of each stage being in asubstantially parallel relationship with each other and zones A, B and Cbeing in a series relationship with zones D, E and F respectivelywherein zones A and D, B and E, C and F can be considered as zone pairseach of said zone pairs being subjected to three equal length butdiscrete cycles, said cycles consisting of (1) an adsorption cycle, (2)a bed pressure equalization to lower pressure to an intermediate level,a dumping to lower the intermediate pressure to a relatively lowpressure resulting in a depressure gas and a purging, and (3) a bedpressure equalization to raise pressure to an intermediate level from arelatively low pressure by bed pressure equalization and subsequentlyraising such intermediate level pressure to a relatively high pressureby using fed wherein at any given instant each of said zone pairs are ona different cycle, D, E and F is effluent from said zones A, B and C andwherein further a first moderately pure product stream is collected fromthe adsorbent zones of stage 1, said first product stream comprising theefiluents obtained from said adsorbent zones of stage 1 and thedepressure gases obtained from the adsorbent zones of stage 2; and asecond relatively pure product stream is collected from the adsorbentzones of stage 2.

13. A process according to claim 12 wherein said bed pressureequalization is carried out by connecting a zone at relatively highpressure with a zone at relatively low pressure.

(2) Reducing said intermediate pressure within said zones C and F to arelatively low pressure;

(3) Purging said zones C and F; wherein said feed stream for the saidzones in said stage 2 is the withdrawn effluent from the zones in saidstage 1 and wherein further a first moderately pure product stream iscollected from the adsorbent zones of stage 1, said first product streamcomprising the effluents obtained from said adsorbent zones of stage 1and the depressure gases obtained from the adsorbent zones of stage 2;and a second relatively pure product stream is collected from theadsorbent zones of stage 2. 7. A method according to claim 6 whereinsaid feed stream for stage 1 zones comprises H 8. A method according toclaim 7 wherein said feed stream comprises hydrocarbons and H 14. Aprocess according to claim 12 wherein said purge with respect to zonesD, E, and F is a portion of primary effluent from said zones.

15. A method according to claim 12 wherein said purge with respect tostage 1 is made up of depressure gas and purge effluent from the secondstage.

16. A process according to claim 12 wherein said feed used for stage 1zones comprises H 17. A process according to claim 12 wherein said feedused for stage 1 zones comprises H and hydrocarbons.

18. A process according to claim 12 wherein said relatively highpressure is attained by using product.

19. A process according to claim .1 wherein said zones A is purged witha purge comprising a portion of purge eflluent from zone B and whereinsaid first moderately pure product stream comprises the diluent of zoneA and purge efiluent from zone B.

References Cited by the Examiner UNITED STATES PATENTS 2,944,627 7/1960Skarstrom 55-62 3,086,339 4/1963 Sk-arstrom 61; al 5562 X 3,102,0138/1963 Skarstrom 5562 X FOREIGN PATENTS 860,311 2/1961 Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

J. ADEE, Assistant Examiner.

1. IN SEPARATION PROCESSES UTILIZING THE PRINCIPLES OF HEATLESSADSORPTION WHEREIN ADSORPTION OF AT LEAST ONE COMPONENT OF A FEED STREAMAT A RELATIVELY HIGH PRESSURE AND DESORPTION OF ADSORBED COMPONENET OFSAID FEED AT A RELATIVELY LOWER PRESSURE IS CARRIED OUT IN AN ADSORPTIONZONE, THE IMPROVEMENT WHICH COMPRISES IN COMBINATION: (A) FLOWING A FEEDSTREAM IINTO ADSORENT ZONE A, SAID ZONE A BEING SELECTIVE FOR AT LEASTONE COMPONENT OF SAID FEED STREAM AND ALLOWING AN EFFLUENT TO EMERGEFROM SAID ADSORBENT ZONE A. (B) FLOWING AT LEAST A PORTION OF SAIDEFFLUENT FROM SAID ZONE A AS FEED EFFLUENT INTO ADSORBENT ZONE B, SAIDZONE B BEING SELECTIVE FOR AT LEAST ONE COMPONENT OF SAID FEED EFFLUENTAND ALLOWING A PRIMARY EFFLUENT TO EMERGE FROM SAID ZONE B. (C)DESORBING SAID ADSORBENT ZONE B BY FIRST LOWERING THE PRESSURE WITHINSAID ADSORBENT ZONE B TO OBTAIN A DEPRESSURE GAS AND THEN PRUGING SAIDZONE B IWTH A PROTION OF SAID PRIMARY EFFLUENT FROM SAID ZONE B. TOOBTAIN A PURGE EFFLUENT. (D) DESORBING SAID ADSORBENT ZONE A BY FIRSTLOWERING THE PRSSURE WITHIN SAID ADSORBENT ZONE A AND SUBSEQUENTLYPRUGING SAID ZONE A WITH A PURGE COMPRISING A PORTION OF DEPRESSURED GASFROM ZONE B. (E) COLLECTION AS A FIRST MODERATELY PURE PRODUCT STREAM ASTREAM COMPRISING THE EFFLUENT OF ZONE A AND THE